Paris mayor says part of museum's security system had been broken since March 30

Paris, France (CNN) -- Interpol has issued a global alert for a Picasso painting and four other works stolen from a Paris art museum -- a sign that authorities believe thieves may have taken the paintings outside the country.

"These extraordinary paintings by these great masters are so recognizable that they will be difficult to sell in any market," Jean-Michel Louboutin, Interpol's executive director of police services, said in a statement released by the agency Saturday.

Prosecutors estimate that the oil paintings nabbed in a heist at the Modern Art Museum in Paris early Thursday morning could be worth 500 million euros ($617 million). In addition to Picasso's cubist "Pigeon with Green Peas," authorities said works by Henri Matisse, Georges Braque, Amedeo Modigliani and Fernand Leger were also stolen from the city-run museum.

Interpol said it had sent images of the paintings to police in 188 countries and also added them to the agency's online database of stolen artwork.

Christopher Girard, an aide to the mayor of Paris who oversees cultural affairs, said whoever stole the paintings entered through a window and was able to thwart guards and video surveillance. The heist showed signs of organized crime, he said.